1. Field of the Invention
The invention is directed to a chamber doctor for inking a cylinder in a printing machine. The cylinder has depressions in its surface for receiving ink. The cylinder can, for example, be a gravure printing, cylinder or a screening roller of a short inking mechanism.
2. Description of the Prior Art
German reference DE 44 25 478 A1 shows a chamber doctor for inking a cylinder in a printing machines which cylinder has depressions for receiving ink. The chamber doctor has doctor blades which adjust automatically to the cylinder depending on wear. In this connection, the doctor blades execute a rotating movement, for which purpose they must be scaled from the chamber doctor body which is stationary relative to the doctor blades, since they form part of the ink chamber. The sealing is effected by a contact seal or in a noncontacting manner as a gap seal. The sealing location is wetted by printing ink which cools during breaks in printing and accordingly becomes viscous. When printing stops for longer periods, e.g., after a day's work, the ink usually dries. The automatic adjustment of the doctor blade is accordingly slowed down or even stopped. As a result, the surface of the inked roller is not wiped clean and too much ink is transferred to the following rollers. This problem can not be solved by increasing the doctor blade adjusting forces since it is not possible to achieve consistent adjusting pressure depending on the degree of stickiness. Moreover a high adjusting force increases wear on the cylinder to be wiped and on the doctor blade. There is also a risk that the doctor blade will buckle.
Another chamber doctor is disclosed in DE 42 13 660 C2. This reference teaches a chamber doctor in which the working doctor blade and the closing doctor blade are each received in a longitudinal slot of the chamber doctor body so as to be displaceable. The blades are pressed by springs against the inked cylinder. Ink penetrates into the guide gap between the doctor blade and the chamber doctor body and completely fills the longitudinal slot. The ink gums up the doctor blades leading to the aforementioned problems.